Mechanisms involved in the transduction of neural signals and the control of tissue specific gene expression are studied. The pineal and pituitary glands are used as model systems. The details of the chemical and ionic components of transmembrane signalling processing and of neural and tissue specific regulation of gene expression are analyzed. Signal transduction in the pineal is of special interest because cAMP and cGMP are regulated by dual receptor mechanisms which appear to interact at the level of regulation of adenylyl and guanylyl cyclases. One leg of these pathways activates these enzymes via GTP binding regulatory proteins, similar to Gs-alpha. In the area of the neural and developmental control of gene expression, advances have been made in purifying N-acetyltransferase and hydroxyindol-O-methyltransferase, and in isolating cDNA clones coding for these enzymes. It has been found that three HIOMT mRNA molecules exist, which appear to be the result of alternative splicing; one contains a truncated LINE sequence in the coding region. The major hormonal product of the pineal gland is melatonin. Melatonin has been found to block GnRH induced increase in [Ca++]i and to block GnRH-induced depolarization. Melatonin appears to act on a subpopulation of GnRH-sensitive cells.